1. Field of the Invention
This invention relates to receiver protectors, particularly to an iris for a gas discharge stage in a receiver protector.
2. Description of the Prior Art
Receiver protectors are used in the microwave duplexing art for permitting the use of a single antenna for transmission of high power output pulses and reception of low power received signals via a common microwave waveguide. Plasma within the receiver protector automatically inhibits the transmission of high power wide bandwidth electromagnetic wave energy in the direction from the antenna to the receiver thus preventing the transmitted pulse from reaching and damaging the receiver. The receiver protector also permits the low power receive signal to come from the antenna through the microwave waveguide to be routed to the receiver. In U.S. Pat. No. 4,027,255 issued on May 31, 1977 to H. K. Blakeney, et al. and assigned to the assignee herein, a three stage receiver protector is described having two gas plasma stages and a diode limiter stage. The second gas plasma stage comprises a first metal gap formed by truncated cones facing one another and a second metal gap formed by an inverted truncated cone and a cone. The cross section of the truncated cone at the gap may be in the range of 0.05 to 0.102 centimeters in diameter with a gap spacing of approximately 0.038 centimeters. When the electromagnetic energy in the gap between a cone and a truncated cone exceeds a firing threshold due to the ionization of the gas, current will flow between the cones short circuiting the waveguide and reflecting energy back towards the input. The reflected energy increases the electromagnetic power density between the two truncated cones which will short circuit when the power density exceeds the firing threshold. The gas selected for the dual cone stage may be a negative attaching gas to permit rapid recovery by extinguishing the gas plasma when the power density in the gaps fall below predetermined levels. Recovery time of the gas plasma or the elimination of gas ions by recombination with electrons is hampered by the limited conducting area of the cones in close proximity to the gap which provide a source of free electrons for recombination with the ions in the gap.
An iris in a waveguide has been used in the prior art to control the passage of electromagnetic energy of a predetermined frequency. In U.S. Pat. No. 2,407,069 issued in 1946 to Fiske a dumbbell iris is described having two circular openings connected by an elongated slot. The two circular openings provide inductance and the elongated slot provides capacitance to form a resonant L-C-L circuit.
It is therefore desirable to reduce the firing threshold of a stage of a receiver protector by utilizing an iris.
It is further desirable to improve the recovery time of a gas plasma in a glass plasma stage of a receiver protector by increasing the area of conducting metal in close proximity of the gap to provide free electrons.
It is further desirable to modify the electric field across the gap of a dumbbell iris to reduce the firing threshold for shunting electromagnetic, radio frequency or microwave power across the gap.